2. HKAL II Q5a compound. F, indicating the expected bond angles around the structures. representation of E

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1 HKAL Past Paper Questions: Part 11 Chemistry of Carbon Compounds Naming and Isomerisms 1. HKAL 1998 II Q5a Consider the following compound F. #(i) (ii) Give the hybridization states of the carbon atoms a, b, c and d. Draw all possible three-dimensional structures for F, indicating the expected bond angles around the carbon atoms a, b, c and d in one of the structures. (5 marks) 2. HKAL 1998 I Q4 Alcohol E has the structure CH 3 CH(OH)C 2 H 5. a. (i) Draw a three-dimensional representation of E (ii) What type of isomerism can be exhibited by E? (2 marks) 1

2 b. (i) Draw the structure of three structural isomers of E, all of which are alcohols. #(ii) Describe how the reagent Zn/concentrated HCl can be used to distinguish E from the three structural isomers. (3 marks) c. On treatment with dilute H 2 SO 4 (aq), E gives mainly two isomeric compounds, F and G, both of which have the formula C 4 H 8. On treatment with bromine, both F and G give a product H with formula C 4 H 8 Br 2. (i) Draw structures for F, G and H. (ii) What is the isomeric relationship between F and G? (4 marks) 2

3 3. HKAL 2008 II Q7a Deduce the structure of isomeric compounds F and G, with formula C 6H12, that have the following characteristics: Compound F Characteristics It has a pair of enantiomers. It loses its chiral centre after hydrogenation over Pt. G It reacts with Br2 to give a single compound. It reacts with HBr to give a single achiral compound. (6 marks) 3

4 4. HKAL 2009 II Q4a The Table below lists the melting points and boiling points of cis-1,2-dichloroethene and trans-1,2-dichloroethene: (i) Explain why, in 1,2-dichloroethene, the carbon-carbon double bond cannot rotate freely. (ii) Explain why (I) cis-1,2-dichloroethene has a higher boiling point, and (II) trans-1,2-dichloroethene has a higher melting point. (6 marks) 4

5 5. HKAL 2010 I Q4 Dimethyl fumarate can be found in most leather products since it is commonly used as a mould inhibitor. However, it was banned in Europe for all kinds of consumer goods in March 2009 because it was found to cause skin allergies. Compound A is an isomer of dimethyl fumarate. The structures and melting points of these two compounds are given below: (a) (i) Name the type of isomerism involved. (ii) Explain why the melting point of A is lower than that of dimethyl fumarate. (3 marks) (b) Both dimethyl fumarate and A can be hydrolysed to their corresponding dicarboxylic acids, B and D. (i) Explain why the melting point of D is lower than that of B. θ (ii) Explain why the Δ of B is more negative than that of D. H f (4 marks) 5

6 6. HKAL I Q5a Consider the reaction: c. Draw the structures of all possible stereoisomers of the product. d. Would the product rotate a beam of plane polarized light? Explain your answer. 7. HKAL 2005 II Q7b The three-dimensional structures of two 2-chlorobutanes (PP and Q) are shown below: (i) (ii) Comment on the difference, if any, in physical properties between P and Q. Will P and Q exhibit the same chemical properties? Explain your answer. (3 marks) 6

7 8. HKAL 1992 I Q1a There are several isomers of benzenedicarboxylic acid. (i) Draw the structures of all possible isomers of benzenedicarboxylic acid. (ii) One of these isomers is used to make terylene. Outline the reaction involved. (iii) On heating, one of the isomers gives a compound W, with formula C 8 H 4 O 3. Give the structure of W. (5 marks) 7

8 9. HKAL 1992 II Q7 A carboxylic acid P, with a relative molecular mass less than 100, contains C, 55.8%; H,7.0%; and O, 37.2% by mass. An attempt to convert P to its methyl ester Q by prolonged refluxing of P with methanol in the presence of aqueous H 2 SO 4 gave the desired ester Q but with much of the starting material P unchanged. a. Determine the molecular formula of P. b. Give the structures of four carboxylic acids having the molecular formula you determined in (a). Give the systematic names for any one of the carboxylic acids and its methyl ester. c. Suggest, with explanations, two ways which would make the esterification go towards completion. d. Which has a higher boiling point, the carboxylic acid or its methyl ester? Explain your answer. e. Show, using equations, how you would convert Q to P. (17 marks) 8

9 10. HKAL 1994 II Q7a What do you understand by the terms structural isomerism and stereoisomerism? (3 marks) 11. HKAL 1994 II Q8c Give a systemic name to each of the following compounds. a. CH 3 CH3CH CH 3 CH CH 2 CH=CH2 b. O CH3CH2CH2-O-C-CH2CH2CH3 c. O CH3CH2-C-CHCH2CH3 OH (3 marks) 9

12. HKAL 1996 II Q8b The following compounds can exist

suitable representations for the isomers. (4 marks) 13.

10 12. HKAL 1996 II Q8b The following compounds can exist in isomeric forms: (i) butenedioic acid, and (ii) 2-aminopropanoic acid. In each case, state the type of isomerism and draw suitable representations for the isomers. (4 marks) 13. HKAL 1999 II Q6c State the relationship between each pair of structures shown below: (3 marks) 10

11 14. HKAL 2002 II Q7b For each of the following pairs of molecules, identify their relationship as identical, enantiomeric, geometrical isomeric or structural isomeric. (5 marks) 11

15. HKAL 2003 II Q6b Compound A (C 6 H 6 O 6 ) is an acyclic tribasic acid isolated from the leaves and tubers of Aconitum napellus. Hydration of A gives two isomeric compounds, B and D.

12 15. HKAL 2003 II Q6b Compound A (C 6 H 6 O 6 ) is an acyclic tribasic acid isolated from the leaves and tubers of Aconitum napellus. Hydration of A gives two isomeric compounds, B and D. B is achiral, but D is chiral. Deduce the structures of A, B and D. (5 marks) 16. HKAL 2006 I Q6c Answer the following multiple-choice question: (i) Which of the following compounds has a pair of enantiomers?? Ans: B 12

13 17. HKAL 2006 II Q5c Deduce the structure of compound D on the basis of the information given below: (1) Elemental analysis data show that D has the following composition by mass: C 40.0%, H 6.7% and O 53.3%. (2) The relative molecular mass of D is estimated to be in the range of 172 to 182. #(3) The infra-red spectrum of D shows, apart from the absorption of C H stretching near 2900 cm -1, a strong and broad absorption around 3400 cm -1, and no appreciable absorption around 1700 cm -1. (4) All carbon atoms of D have the same bonding environment. (5) D is highly soluble in water, and the solution does not decolorise bromine water. (8 marks) 13

14 18. HKAL 2006 II Q5b Compound B is a strong stimulant. Its structural formula is as follows: (i) Give the systematic name of B. (ii) In fact, the above structural formula can represent two stereoisomers. (I) (II) Draw three-dimensional structures of the two stereoisomers. State a physical property which is different for the two stereoisomers. (iii) It is known that among the two stereoisomers, only B has stimulant activity while the other one does not. Why? (iv) A person is suspected to have taken stimulant B. A urine sample of the person is sent for analysis. Suggest a method to establish whether B is present in the urine sample. (7 marks) 14

15 Alkanes and Alkenes 19. HKAL 1999 I Q5a Under certain conditions, methane reacts with chlorine to give chloromethane as the major product. (i) State the conditions for the reaction (ii) Outline the mechanism and name the mechanistic steps of the reaction. (iii) Is the reaction of methane with chlorine an appropriate method for the preparation of dichloromethane? Explain. (5 marks) (i) (ii) (iii) 15

16 20. HKAL 2001 I Q5a Consider the reaction: (D is deuterium, as isotope of hydrogen) (i) Draw the structure of the major product. (iii) Is the product optically active? Explain your answer. (3 marks) (i) (iii) 21. HKAL 2001 I Q6b After some lessons in organic chemistry, a student remarked, Alkanes are more stable than alkenes, therefore alkanes do not react with chlorine but alkenes do. Do you agree with the student? Explain. (3 marks) 16

17 22. HKAL 2004 II Q6b Hydrocarbons G reacts with HBr to give J as the major product. (i) (iii) Give the structure of J and its systematic name. A student commented that J obtained from the above reaction is optically active. Do you agree with the student? Explain. (5 marks) (i) (iii) 23. HKAL 2005 I Q6b (iii) Which of the following statements concerning the hydrogenation of ethene is INCORRECT? A. The hydrogenation is an exothermic process. B. The hydrogenation occurs in the presence of a catalyst at room temperature. C. The H-H bond is weak to allow the hydrogenation to occur. D. Ethane is less energy rich than the starting materials. Ans: C 17

18 24. HKAL 2007 I Q5a (ii) Give the structure of the major organic product E in the following reaction. Indicate the stereochemistry of the products as appropriate. (1 mark) 25. HKAL 2007 II Q7b Consider the following reaction: (i) Give the structure of the major organic product L. (1 mark) 18

19 26. HKAL 2009 II Q4b Neoprene, a synthetics rubber, can be obtained from buta-1,3-diene via the following route: #(i) The reactant for Step 1 is Br 2. Propose a mechanism for the formation of A from buta-1,3-diene. (ii) Suggest reactant(s) and conditions for each of Steps 2,3 and 4. #(iii) Explain why the strength of neoprene can be improved after heating it with sulphur. (8 marks) 27. HKAL 1995 II Q9b Identify the following unknown structure. M CH 2 =CHCO 2 CH 3 CH 3 CH 2 CO 2 CH 3 (1 mark) M: Pd or Ni or Pt / H 2 19

20 28. HKAL 1991 II Q7a State with explanations, what you would observe in each of the following experiments, and write equations for the reactions. (i) (ii) A mixture of pentane and bromine in tetrachloromethane is exposed to sunlight. Propene is bubbled into aqueous alkaline potassium manganate(vii). (i) The reddish brown bromine turns colourless (1) The reaction is a free-radical substitution reaction (0.5) Depending on the amount of bromine, various substitution products are obtained. CH 3 CH 2 CH 2 CH 2 CH 3 + Br 2 CH 3 CH 2 CH 2 CH 2 CH 2 Br or CH 3 CH 2 CH 2 CH 2 CHBr 2 etc (1) (ii) The purple colour of KMnO 4 turns to colourless. (1) KMnO 4 is reduced and the alkene is oxidized. (0.5) OH OH CH 3 CH=CH 2 KMnO 4 H 3 C C C H (1) H H 29. HKAL 1998 II Q5c Give the structures of the major organic products, G and H, in (i) and (ii) below. #Outline a mechanism for the formation of the major product in each of the three reactions. (i) (ii) (2 marks) (i) CH 3 G: H 3 C C Br CH 2 CH 3 (ii) H: CH 3 CH 2 CH 2 OH 20

21 Alkanols, Ketones/Aldehydes and Carboxylic acids 30. Show how you carry out the following conversions in the laboratory, giving the structures of intermediate compounds and the reagents for each step. a. HKAL 1995 II Q8b(ii) OH CH 3 CH 2 CH 2 OH H 3 C C CH 3 H (3 marks) b. HKAL 1996 II Q9a(iv) OH OH OH (3 marks) 21

22 31. Outline chemical tests which would allow you to distinguish between the compounds in the following pairs. Describe what you would observe in each case. a. HKAL 1991 II Q9a (ii) COOH OH (2 marks) Add solution of NaHCO 3 to the compound, C 6 H 5 COOH will react to give CO 2 while the phenol C 6 H 5 OH will not. b. HKAL 1991 II Q9a (iv) OH H CH 3 CH 2 CH 2 C CH 3 CH 3 CH 2 CH 2 C CH 2 OH CH 3 CH 3 (2 marks) Warm the compounds with acidified K 2 Cr 2 O 7. The primary alcohol will turn the solution from orange to green while the tertiary alcohol will not. c. HKAL 1993 II Q8a(iv) OH CH 2 OH CH 3 (3 marks) Warm the compounds with acidified K 2 Cr 2 O 7. The primary alcohol will turn the solution from orange to green while the tertiary alcohol will not. 22

23 d. HKAL 1995 II Q7a(iii) CH 3 OH CH 2 OH (4 marks) e. HKAL 1993 II Q8a(ii) CH 3 CH 2 CH 2 CH 2 CHO CH 3 CH 2 COCH 2 CH 3 (3 marks) Warm the compounds with acidified K 2 Cr 2 O 7. The aldehyde will turn the solution from orange to green while the ketone will not. f. HKAL 1996 II Q7c O O C H (2 marks) 23

24 32. HKAL 1996 II Q7b In an experiment, 25 g of (CH 3 ) 3 COH react with 36 g of HCl to gives 28 g of (CH 3 ) 3 CCl. (i) Find the limiting reactant of the reaction,showing clearly your calculation. (ii) Calculate the percentage yield of (CH 3 )CCl. (3 marks) 24

25 33. HKAL 2000 II Q7a An acyclic compound, R(C 7 H 12 O) has a linear structure, R can be converted to S and then to T: C 7 H 12 O LiAlH 4 C 7 H 14 O H 2 /Pd C 7 H 16 O R S T Given that R exists as a mixture of geometrical isomers, S has a chiral carbon center, and T does not have any chiral carbon center, deduce all possible structures of R, S and T. (8 marks) 25

26 34. HKAL 2001 I Q8b In an experiment to prepare propanal from propan-1-ol, CH 3 CH 2 CH 2 OH Cr 2 O 7 2- / H + heat CH 3 CH 2 CHO a side-product N (C 6 H 12 O 2 ) was formed. (i) What is N? Suggest how N is formed. (ii) Suggest one method to separate propanal from a mixture of propanal and N. (iii) Suggest two methods to confirm the identity of propanal. (3 marks) (i) (ii) (iii) 26

27 35. HKAL 2002 I Q5b Suggest reagent(s) to accomplish each of the following single-step transformations: (1 mark) 36. HKAL 2005 II Q6a Formaldehyde (methanal) is one of the commonly found organic indoor air pollutants. (i) Suggest a source of household formaldehyde. #(ii) The indoor air quality (IAQ) standard for formaldehyde has been set at 0.10 ppm by volume. Calculate the maximum allowable quantity of formaldehyde, in gram in a room of volume 200 m 3 at 298 K and N m -2. (You may assume that formaldehyde behaves as an ideal gas.) (iii) Some indoor air purifiers remove formaldehyde by chemical means. Suggest one chemical for the removal of formaldehyde with the formation of less harmful products. (iv) Name one other organic indoor air pollutant and suggest its source. (7 marks) 27

28 37. Identify the following unknown structure. a. HKAL 1994 II Q7 CH 3 CH=CHCH 2 CH 2 COOH LiAlH 4 (1 mark) CH 3 CH=CHCH 2 CH 2 CH 2 OH b. HKAL 1995 II Q9b(ii), (iv) (ii) CH 3 CH 2 CH 2 COOH L CH 3 CH 2 CH 2 COCl (1 mark) (iv) HOCH 2 CH 2 OH N O C O C OCH 2 CH 2 O n (1 mark) 28

29 38. HKAL 2002 II Q7d Suggest a synthetic route, in not more than three steps, for the transformation of 3-methylbenzoic acid to N,N-diethyl-3-methylbenzamide, a substance commonly used in mosquito repellant. CO 2 H CON(CH 2 CH 3 ) 2 CH 3 CH 3 3-methylbenzoic acid N,N-diethyl-3-methylbenzamide (2 marks) 39. Identify the following unknown structure. a. HKAL 1993 II Q7a(iii) NH 2 CH3COCl (1 mark) O H N C CH 3 b. HKAL 1994 II Q7 NH 2 CH3CH2COCl (1 mark) N O 29

30 40. HKAL 1997 II Q5b The following equation representss the acid hydrolysis of a dipeptide D to produce compounds E and F, one of which is chiral compound. (i) (ii) (iii) Name all functional groups in D. Give one structure for E and one for F. Draw a suitable representation for the chiral product. Suggest a method to separate E and F from the reaction mixture. (5 marks) 30

31 41. HKAL 2007 I Q4a, b (a) Consider the alkaline hydrolysis shown below: Give the structure of product A. (1 mark) (b) Consider the acidic hydrolysis shown below: (i) Give the structure of product B, (ii) Suggest the amount of acid required for the hydrolysis of 1 mole of the ester. Explain your answer. (2 marks) a. b. (i) (ii) 31

32 42. HKAL 2009 I Q8 3-Methyl-l-butydistinctive pleasant banana odour and is used in food flavouring. In an experiment to prepare the compound, 5.0 cm 3 of isoamyl alcohol is allowed to react with l5.0 cm 3 of glacial acetic acid in the presence of a reagent ethanoate, commonly knownn as isoamyl acetate, is a naturally occurring compound having a L. (a) Suggest what reagent L may be and give the reaction conditions for this preparation. (l mark) (b) Calculate the mole ratio of isoamyl alcohol to glacial acetic acid used in this preparation. (Given: density of isoamyl alcohol=0.81 g cm -3 ; density of glacial acetic acid =1.05g cm -3 (2 mark) (c) Draw a labelled diagram of the assembly of apparatus used in this preparation. (2 mark) (d) What are the major compounds present in the resulting mixture at the end of this preparation? (l mark) (e) Outline the procedures to isolate isoamyl acetate from the resulting mixture. (It is known that isoamyl acetate cannot be effectively separated from the resulting mixture by fractional distillation..) (3 marks) (f) Suggest why isoamyl alcohol is NOT used in excess in this preparation. (l mark) 3 ) 32

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34 43. HKAL 1991 II Q9b Suggest a possible structure for each of the compounds J, K and L below and explain briefly your deductions. (i) J, C 4 H 6 O, on oxidation gives K, C 4 H 6 O 2. (2 marks) (ii) L, C 5 H 12 O, can exist as a pair of enantiomers, and reacts with phosphorus pentachloride to give hydrogen chloride. (2 marks) (i) (ii) 34

35 Important Organic Chemicals 44. HKAL 2002 II Q7c A mixture of 2.8 g of butane-1,4-diol and 6.3 g of benzene-1,3-dicarbonyl chloride was heated at 215 o C for 30 minutes to give 6.4 g of a polymer M. COCl HO(CH 2 ) 4 OH COCl butane-1,4-diol benzene-1,3-dicarbonyl chloride (i) Draw the repeating unit of M. (ii) What type of polymerization is involved in the formation of M? (iii) Calculate the percentage yield of M. (5 marks) 35

36 45. HKAL 1997 II Q6b Saponification of 1 mol of fat G with NaOH(aq) produces 1 mol of a triol C 3 H 8 O 3, 2 mol of CH 3 (CH 2 ) 16 CO - 2 Na + and 1 mol of CH 3 (CH 2 ) 14 CO - 2 Na +. (i) If G is optically active, suggest its structure. Explain. (ii) If G is optically inactive, suggest its structure. (iii) What is the minimum number of moles of base required for the complete saponification of 1 mol of G? (4 marks) 36

37 46. HKAL 1999 II Q5c Dacron is the most common of the group of polymers known as polyesters. A segment of the polymer chain is shown below. (i) Suggest two types of material which can be made from polyesters. (ii) Draw the structures of the two monomers used in manufacturing Dacron. Name involved. (iii) How can Dacron be degraded in the environment? the type of polymerization (5 marks) 37

38 47. HKAL 1999 II Q6b (i) Draw the structure, showing two repeating units, for each of the following polymeric materials: (I) poly(chloroethene) and (II) cellulose (ii) Large quantities of poly(chloroethene) and cellulose used in daily life, Suggest, with explanation, an appropriate waste disposal method for each material. (5 marks) 38

39 48. HKAL 2000 II Q6 a. Sodium stearate CH 3 (CH 2 ) 16 CO - 2 Na +, the most common soap, can be made by heating a triglyceride with sodium hydroxide solution. (i) Draw the structure of the triglyceride. (ii) With the help of equation( (s), describe the chemistry when soap is added to hard water. (iii) Explain why washing soda, Na 2 CO 3. 10H 2 O, can help to reduce the hardness the water. (4 marks) b. Product J, from the transformation below, is commonly-used household detergent. (i) (ii) (iii) Draw the structure of J. State one advantage of using J as a detergent. State one environmental problem associated with the use of J. (3 marks) 39

40 c. Dodecyl glucoside is a new detergent. (i) (ii) Explain why dedocyl glucoside can be used in the cleansing of oily dirts. Suggest how dodecyl glucoside can be degraded in the environment. (4 marks) 40

41 49. HKAL 2005 II Q5b Aspartame is a commonly used artificial sweetener. (i) (ii) (iii) Copy the structure of aspartame into your answer book, and mark each chiral carbon atom with an asterisk. With referencee to its structure, explain why aspartame is unstable in cooking. In a coffee shop, a packet of sweetener contains about 5% of aspartame and 95% of silicon dioxide. Suggest a reason for including silicon dioxide in the packet. (4 marks) 41

42 50. HKAL 2006 II Q7a In the past, people chewed willow bark to ease their pain and to lower fever. Later on, chemists identified salicin as the active ingredient in willow bark. salicin Salicin undergoes acid hydrolysis to give glucose and 2-hydroxybenzyl alcohol. #(i) Suggest a chemical test to distinguish between salicin and glucose. Account for the difference in results of your suggested test. (ii) 2-Hydroxybenzyl alcohol can be converted in two steps to acetylsalicylic acid, which is the active ingredient of aspirin. 2-hydroxybenzyl alcohol acetylsalicylic acid (I) Give the reagents used in Step 1 and in Step 2. (II) In a typical experiment, 2.0 g of 2-hydroxybenzyl alcohol gives 2.0 g of acetylsalicylic acid. Calculate the percentage yield of the conversion. (7 marks) 42

43 51. HKAL 2007 II Q6d Polyethene terephthalate (PET) is a polymer used in making clothing fibres and soft drink bottles. The flow diagram below shows a route for the synthesis of PET. (i) Give the reagent(s) and conditions for each of Steps 1, 2, 3 and 4. (ii) Polyethene naphthalate (PEN) is a polymer formed from naphthalic acid and ethane-1,2-diol. (I) (II) Draw the structure of a repeating unit of PEN. Which polymer, PET or PEN, do you expect to be more rigid? Explain. (6 marks) 43

44 52. HKAL 2010 II Q4d Polyethylene terephthalate (PET) is a polymer commonly used in making soft drink bottles. (i) Suggest a synthetic route with no more than three steps to convert benzene-1,4-dicarbaldehyde to PET. (You are NOT allowed to use organic reagents with more than three carbon atoms.) (ii) Suggest why PET as compared with polystyrene, is more readily degraded in the environment. (4 marks) 44

45 Miscellaneous 53. HKAL 2000 II Q6e Identify L, M and N in the following reactions: 45

46 54. HKAL 2002 II Q5c Consider the substances listed below: butane benzoic acid dichlorodifluoromethane ethanoic acid hexane polystyrene propanone tetrachloromethane triethylamine For each of the descriptions of physical properties from (a) to (h) below, choose from the above list, one substance which best fits the description. (i) a colourless, flammable gas (ii) a colourless liquid with a sour odour (iii) a colourless, water miscible, flammable liquid (iv) a colourless, non-flammable liquid (v) a colourless liquid with a fishy smell (vi) a colourless, water immiscible, flammable liquid (vii) a white solid which is insoluble in both cold and hot water (viii) a white solid which is insoluble in cold water, but soluble in hot water (8 marks) 46

47 55. HKAL 2003 I Q6b The weakest chemical bond in an organic compound always breaks first in a chemical reaction. The above statement is not always true. Give one example for which the statement is true and one example for which the statement is not true. Explain each case briefly. (4 marks) 47

Chemistry 2.5 AS WORKBOOK. Working to Excellence Working to Excellence

Chemistry 2.5 AS WORKBOOK. Working to Excellence Working to Excellence Chemistry 2.5 AS 91165 Demonstrate understanding of the properties of selected organic compounds WORKBOOK Working to Excellence Working to Excellence CONTENTS 1. Writing Excellence answers to Cis-Trans